Gas turbines typically include a compressor, a combustor and a turbine. The compressor pressurizes air flowing into the turbine. Pressurized air is discharged from the compressor and flows to the combustor. Air entering the combustor is mixed with fuel and combusted. Gas turbine engines operate by combusting fuel with compressed air to create heated gases. The heated gases are used to drive a turbine for rotating a fan to provide air to the compressor. Additionally, the heated gases are used to drive a turbine to power the compressor. In a turbo fan engine a low-pressure turbine powers a fan which produces a majority of the thrust.
The fan pushes air into a nacelle where part of the incoming air is directed to the core engine while the majority of the incoming air bypasses the core engine. The air that bypasses the core engine is known as bypass air, and is responsible for majority of the thrust for propelling the aircraft in flight. The air which is directed to the core engine is compressed and combusted and is typically referred to as the core flow. In some core engines, there is an intermediate compressor and a high pressure compressor. The efficiency of the core engine is limited by the air temperature entering the high pressure compressor. The high pressure compressor will work more efficiently if it is compressing cooler air. By cooling the core flow, the cycle is changed because cooler air will also allow the cycle to go to a higher pressure.
Heat exchangers can be employed in a gas turbine engine for the purpose of transferring heat between the core air stream and a fan bypass airstream. Some systems place the heat exchanger directly in the flow of the fan bypass airstream. Although this type of arrangement provides sufficient airflow for cooling there is a penalty in drag and pressure loss. Providing sufficient airflow in a secondary duct is also a challenge because of flow rate requirements for meaningful heat transfer. Dump losses result when fan bypass air is bled into a secondary duct. The heat exchanger can also cause a significant pressure loss. When the cooling benefits have been obtained through the use of a heat exchanger they are at least partially offset by propulsion losses.
Pressure losses result when the dynamic pressure of the air stream becomes static pressure as the air enters the chamber as well as the resistance in flow from the heat exchanger. Lost thrust can occur when the air stream is discharged from the secondary duct. However it would be desirable to provide a method and system for intercooling a turbo fan engine by employing a secondary duct with suitable flow and minimal pressure loss.
For the purposes of this discussion, the definition of a microchannel heat exchanger may be a heat exchanger which contains one or more passages with hydraulic diameters in the range of 10 microns to 200 microns. The definition of minichannel heat exchanger may be a heat exchanger which contains one or more passages with hydraulic diameters in the range of 200 microns to 3000 microns.
For the purposes of promoting an understanding of the principles of the embodiments, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the embodiments is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the embodiments as described herein are contemplated as would normally occur to one skilled in the art to which the embodiment relates.